It is a common problem of all floor joist formwork that its installation is a relative easy process in that the individual elements can be assembled on the ground, then lifted by a crane to the job site where they can be erected with relative ease with the aid of supports, while after completion of the concreting work the formwork must as a rule be removed by hand because it is no longer accessible by the crane due to the freshly concreted floor.
To permit the removal of known joist formwork a relatively important clearance is required. Therefore, to permit stripping of the lateral surfaces of the joist it will often be necessary to remove parts of the floor formwork. Further, the joist formwork is often provided with arms or plates projecting outwardly from their upper ends which are then propped by braces so that the latter finally bear the whole joist formwork. All these constraints have in the known joist formwork systems led to designs which do not exactly facilitate the installation of the formwork and are very difficult to remove. In known joist formwork systems, the side form elements are held together by joist clamps embracing them, the yokes of the clamps being adapted to be fastened to the frame pieces at selective heights. In a joist formwork of the said type known from a brochure of the firm Ischebeck, namely Titan U, the side bars and the yoke of the joist clamp must be adjusted to the height and width of the joist and then rigidly connected with each other, prior to installation of the clamp. Thereupon, the sheathing boards are nailed to the side bars and the yoke of the clamp, and plates arranged at the upper end of the side bars of the clamps are interconnected by squared timber. The finished form, now completely stiff, is then moved by a crane to the job site to be erected with the aid of braces acting upon the squared timber. Since this type of joist form is completely rigid at the site where it is used, it can be hardly clamped together with the floor form for the purpose of sealing the joints. In addition, making this type of joist form and installing it in the floor form requires a substantial amount of work hours. Moreover, this prior art joist form is also extremely heavy and no longer suited for handling by manual labour.
A similar design offered by the firm of Heilwagen which likewise uses the principle of the clamp embracing the formwork and which is also completely assembled on the ground and then moved by a crane to the job site, is said to facilitate the stripping work in that the side bars can be laterally displaced a certain distance at the crossing points between the side bars and the yoke of the joist clamp embracing the lateral form elements, and also lowered a certain distance so as to provide sufficient clearance between the individual elements of the joist formwork and the freshly cast joist to enable the side form elements to be removed. As mentioned before, however, this known formwork comprises plates projecting outwardly from the upper end of the side form elements for being supported by beam-shaped longitudinal girders which in turn are propped by braces. So, these braces must be removed first as they would otherwise prevent any lateral displacement of the side form elements. This means, however, that the yoke of the subfloor clamp must be necessarily supported before these braces are removed, for instance by means of the lifting truck mentioned in the relevent brochure which then serves to remove the formwork as one unit, without having been taken apart.